Radar sensors are increasingly used in motor vehicles, which serve to detect the surrounding traffic in order to furnish data for various driver assistance functions, for example, for adaptive cruise control or for a lane change assistant.
Frequently, it is desirable to install the radar sensor hidden behind a trim component, for example, a bumper of the motor vehicle. In such a case, however, it must be expected that a portion of the microwaves which penetrate the bumper are reflected on this bumper, thereby reducing the performance and, therefore, the range of the radar sensor. More importantly, the waves reflected on the bumper and received back by the radar sensor for the evaluation of the actual radar signal form an interfering signal. This makes it more difficult, particularly in the case of angle-resolving radar sensors, to measure the angular position of the located radar targets.
In the case of plastic bumpers made homogeneously of a uniform material, it is possible to design the thickness of the plastic wall forming the bumper in such a way that the reflected waves are largely eliminated as a result of resonance effects and interference effects. Such a design is impracticable, however, in the case of trim components having a multilayer structure, for example, in the case of painted bumpers.